Preprocessor directives

Refer to (http://www.cplusplus.com/doc/tutorial/preprocessor/)

Preprocessor directives are lines included in the code of programs preceded by a hash sign (#).
Using backslash (\) to continue the current line.

It includes :
[1] macro definitions
#define, #undef

[2] conditional inclusions
#ifdef, #ifndef, #if, #endif, #else and #elif

[3] line control
#line

[4] error directive
#error

[5] source file inclusion
#include

[6] pragma directive
#pragma

[7] predefined macro names
__LINE__
__FILE__
__DATE__
__TIME__